This is something I have been pondering for awhile. I am 6'4 250 ride a KLR but want a much larger tent. Right now I am using a Eureka Apex 3man tent. While it packs small it's also a PITA for me to move around in. And when I take my wife or one of my kids with me overnight it's way to small..
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you've already got the ideal tent layout (free standing, high ceiling, easy setup, stable, etc).. but following the rule of going down one person. your 3 man tent is really sized for two.

you'd probably be happy with same tent in a 4 person size. which is really sized for 3 ... make sure you get aluminum poles. quite a difference in weight/strength... note tent below has fiberglass poles. you want the aluminum pole version.